Editing VEB Robotron (section)

==K 1520 bus standard==
The K 1520 bus was an early [[computer bus]], created by VEB Robotron in 1980 and specified in TGL 37271/01.<ref>{{cite web|url=https://katalog.ub.uni-weimar.de/tgl/TGL_37271-01_07-1980.pdf|archive-url=https://web.archive.org/web/20221205171144/https://katalog.ub.uni-weimar.de/tgl/TGL_37271-01_07-1980.pdf|title=TGL 37271/01 - Microcomputer System Bus line Interface BUS K 1520 System Bus|archive-date=December 5, 2022}}</ref> It was the predominant computer bus architecture of microcomputer-sized systems of [[East Germany]], whose industry relied heavily on the [[U880]] microprocessor, a clone of the [[Zilog Z80]].

Among the large number of boards developed using the standard<ref>{{cite web | url=https://www.robotrontechnik.de/index.htm?/html/standards/k1520.htm | title=www.robotrontechnik.de - K1520-Standard }}</ref> were CPU modules, [[Random Access Memory|RAM]] modules, graphics cards, [[Magnetic-tape data storage|magnetic tape]] controllers and [[floppy disk controller]]s.

It was originally intended to be used to connect boards to backplanes, as in the {{ill|Mikrorechnersystem K 1520|de|Mikrorechnersystem K 1520|lt=K 1520}} modular microcomputer system,  [[A 5120]] office computer, A 5130 office computer<ref>{{cite web | url=https://www.robotrontechnik.de/index.htm?/html/computer/a5130.htm | title=www.robotrontechnik.de - Die Geschichte der Computertechnik der DDR }}</ref> and the [[Poly-Play]] arcade cabinet.

But it was also used as an expansion bus for computers that featured a [[mainboard]] such as 
* [[PC 1715]] office computer - with 2 internal slots, one being occupied by the floppy disk controller
* [[KC 85]]/2, KC 85/3, KC 85/4 [[microcomputer]]s - with two internal slots for expansion cartridges and one back-side connector for:
** D002 - expansion unit for 4 additional expansion cartridges
** D004 - a floppy controller subsystem plus 2 cartridge slots
* [[Robotron KC 87|KC 87]] microcomputer - a.k.a. Z 9001 and KC 85/1
* [[Robotron Z1013|Z 1013]], a [[home computer]] - consumer product in kit form
* BIC A 5105 [[:de:Bildungscomputer robotron A 5105|[de]]] educational microcomputer - not produced in significant quantities
* [[Amstrad CPC#KC compact|KC compact]] late home computer - not produced in meaningful quantities

[[File:Bauelementeträger Z 1013.jpg|thumb|upright=0.6|K 1520 bus expansion for Z 1013]]
The bus had 58 pins and was commonly physically represented by a two-row connector with 29 pins each. The following signals and connections were used:
* DB0 ... DB7 (bidirectional data bus)
* AB0 ... AB15 (address bus)
* /MREQ, /IORQ, /RD, /WR, /RFSH, /M1, /WAIT, /HALT, /INT, /NMI, /BUSRQ, /RESET (Z80 control signals)
* /BAI, /BOA /BUSACK (bus priority chain)
* /IEI, IEO (interrupt enable priority chain)
* /IODI, /MEMDI, /RDY (access control)
* clock, +5V, -5V, +12V, ground